1. Field of the Invention
The present invention concerns ball-joint devices and in particular devices for mounting a mobile part of a headlamp, such as a reflector, on a relatively fixed part to enable adjustment of the mobile part.
2. Description of the Prior Art
Conventionally a mobile part of this kind has a plurality of (typically three) spherical cavities adapted to receive complementary spherical heads at the end of screwthreaded rods or the like. Rotation of one rod causes axial displacement of the head and thus pivoting of the mobile part, for example to adjust the lightbeam emitted by the headlamp in bearing and in azimuth.
The head is conventionally forced or "snapped" into its cavity during assembly, the walls of the cavity having the elasticity required to allow this and then to hold the head so that its movements are effectively transmitted to the mobile part.
It is known for the cavity to be defined by an intermediate member or capsule attached to the mobile part to which it is clipped by flexible lugs or the like providing mutual inter-engagement.
The document FR-A-2 351 350 discloses a construction of this type.
This prior art construction has a number of drawbacks, however. Firstly, the clipping of the capsule to the mobile part such as a reflector usually results in some play or clearance which causes undesirable variations in the effective orientation of the beam. Also, there may additionally be play between the spherical head and its cavity. Moreover, the flexibility of the capsule material, which is necessary to allow the previously mentioned snap action, is such that there is a high risk of the head separating from the capsule if excessive loads are exerted on these members, in particular when the mobile part reaches the end of its authorized travel.
The document EP-A-0 356 750 describes a ball-joint device intended to avoid this problem in which flexible non-return lugs are provided for holding the spherical head at the bottom of its seat.
This prior art solution effectively reduces the risk of separation but as the non-return lugs are normally in contact with the ball and therefore in part define the seat for said ball, any manufacturing tolerance or clearance between these lugs and the bottom of the seat in turn causes clearance in the positioning of the ball, which is undesirable for the reasons stated above.
The present invention is intended to alleviate these drawbacks of the prior art.